1. Field of the Invention
The present invention relates to a stacked coil device, and more particularly, to a coil device capable of being used as a transformer, a common mode choke coil, and etc.
2. Description of the Conventional Art
Generally, it is important to increase an electromagnetic coupling between a first coil and a second coil in order to enhance an electrical characteristic of a coil device such as a common mode choke coil or a transformer. To increase the electromagnetic coupling between the first and second coils, an interval between the first and second coils has to be small or a magnetic path has to be formed not to generate a leakage flux.
FIG. 1A is a perspective view showing a common mode choke coil including a coil device in accordance with the conventional art, and FIG. 1B is a disassembled view of the common mode choke coil of FIG. 1.
As shown in FIG. 1A, the common mode choke coil 1 includes a stack body 7 formed at an upper portion of a first magnetic substrate 3, a second magnetic substrate 10 formed at an upper portion of the stack body 7, an adhesive layer 8 formed between the stack body 7 and the second magnetic substrate 10, and an external electrode 11 formed at outer surfaces of the first magnetic substrate 3, the stack body 7, the adhesive layer 8, and the second magnetic substrate 10.
As shown in FIG. 1B, the stack body 7 includes a plurality of layers evaporated by a thin film forming technique such as a sputtering. An insulating layer 6a formed of a non-magnetic insulation material such as a polyimide or epoxy resin is evaporated on the first magnetic substrate 3, leading electrodes 12a and 12b are formed on the insulating layer 6a, another insulating layer 6b is formed on the leading electrodes 12a and 12b, a coil pattern 4 and a leading electrode 12c extending from the coil pattern are formed on the insulating layer 6b, another insulating layer 6c is formed on the coil pattern 4 and the leading electrode 12c, and a coil pattern 5 and a leading electrode 12d extending from the coil pattern are formed on the insulating layer 6c. 
One end of the coil pattern 4 is electrically connected to the leading electrode 12a through a via hole 13a formed on the insulating layer 6b, and the leading electrode 12a is electrically connected to the external electrode 11a. The other end of the coil pattern 4 is electrically connected to the external electrode 11c through the leading electrode 12c. 
Meanwhile, one end of the coil pattern 5 is electrically connected to the leading electrode 12b through the via hole 13c formed on the insulating layer 6c and the via hole 13b formed on the insulating layer 6b, and the leading electrode 12b is connected to the external electrode 11b. The other end of the coil pattern 5 is electrically connected to the external electrode 11d through the leading electrode 12d. 
In case of inserting said coil device to a circuit, each external electrode 11 is electrically connected to each connecting portion of the circuit, so that the coil patterns 4 and 5 are connected to the circuit.
Since said device is fabricated by a thin film forming technique such as a sputtering or an evaporation, an interval between the first and second coils can be small up to several μm. According to this, an electromagnetic coupling becomes greater than the conventional one and the device can become small, but an expensive equipment is required and a productivity is degraded.
Also, in the coil device of FIGS. 1A and 1B, the non-magnetic insulating layer 6c is positioned between the coil pattern 4 and the coil pattern 5. Accordingly, a leakage flux is generated thus to have a limitation in increasing an electromagnetic coupling and an impedance characteristic.